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Project ID: 17-2-01-8

Year: 2017

Date Started: 07/01/2017

Ending Date:  06/30/2019

Title: Controls of post-fire N retention in California chaparral: mammalian herbivores and ephemeral herbs

Project Proposal Abstract: Nitrogen, which is integral to plant structure and photosynthesis, is limiting to plant growth in many natural ecosystems. During crown fire in California chaparral shrublands, large net losses of nitrogen occur through volatilization from biomass, litter, and soils. However, the ash layer deposited on chaparral soils is rich in ammonium (NH4+). The onset of winter rain stimulates the rapid conversion of ash-derived ammonium (NH4+) to nitrate (NO3-), a form of nitrogen that is highly soluble and mobile in soils. If not absorbed immediately by plants, soil nitrate can be lost from chaparral through leaching and runoff, polluting nearby bodies of water and slowing shrub recovery. In the first two years after chaparral fire, fast-growing herbaceous species often dominate the landscape. While it has been suggested that these ephemeral plant communities play an important role in retaining ash-derived nitrogen in the years after fire, no herb-removal experiment has been conducted to directly test this hypothesis. In this investigation, we will introduce a large-scale herb-manipulation experiment. In 3mx4m plots, we will remove select herbaceous seedlings, so that plots contain (1) All naturally-occurring herbs, (2) Non-N-fixers only, (3) N-fixers only, or (4) No herbs. We will measure the impact of both herb abundance and functional-group composition on post-fire N cycling in chaparral. In tandem to these manipulated plots, we will establish fenced exclosures to evaluate the effect of mammalian herbivores on herbaceous plant composition and nutrient cycling. In high-N systems, herbivores are predicted to accelerate N cycling and increase N retention. In both experiments, N cycling will be measured through mineralization rates, total soil N, decomposition rates, and shrub nitrogen status. The parallel design of these two manipulative experiments will elucidate how herbivore-mediated shifts in post-fire herb communities may influence nitrogen retention in chaparral. Testing theories in natural settings, like post-fire chaparral, increases their generalizability to other ecosystems. Understanding the impact of mammalian herbivores on post-fire nitrogen retention will suggest where to exclude or introduce grazers, ultimately promoting shrubland recovery and protecting aquatic health. We will present the conclusions of this investigation to CalFire vegetation management planners and members of the Northern CA Prescribed Fire Council, through a joint workshop with the California Fire Science Consortium.

Principal Investigator: Wayne P. Sousa Ph.D.

Agency/Organization: University of California-Berkeley

Branch or Dept: Department of Integrative Biology

Other Project Collaborators




Branch or Dept

Agreements Contact

Noam Pines

University of California-Berkeley

Sponsored Projects Office

Budget Contact

Noam Pines

University of California-Berkeley

Sponsored Projects Office

Student Investigator

Lindsey G. Hendricks-Franco

University of California-Berkeley

Department of Integrative Biology

Project Locations

Fire Science Exchange Network









State Lands

Project Deliverables

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Supporting Documents

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